The heavy plate rolling process needs accurate predictions of the process parameters. The plate thickness, flatness and rolling stability are of this direct influenced as well as the productivity. Therefore, careful calculation of the process parameters and pass schedules is necessary. The thesis is concerned with two aspects of controlling rolling; the choice of optimal pass schedules and roll wear. A software has been developed in Paper A to determine optimal pass schedules for thermomechanical rolling in order to obtain a fine microstructure. It includes models of the effect of strain, precipitates, static and dynamic recrystallization and austenite grain size on the final grain size. The predicted grain sizes for four different cases were compared with experimental results. It was also used to study the effect of different delay times during the pass schedule of rolling thermomechanical plate. The results shows that an increase in delay times results in finer ferrite grains are received. The refinement is however small for long delay times. Long delay times also affect the productivity negatively. A method for modeling of the work roll contour in a four high mill is presented in Paper B. The active parameters were found to be the plate length and the variations of the pressure from the plate and the back-up roll on the work roll along the work roll barrel. The method is build up with statistical methods. The bases for the statistics are simulations of different rolling cases and measurements from the production of heavy plates in Oxelösund. The proposed wear contour model was found to be in good agreement with the measurements from the production. / <p>Godkänd; 2006; 20061206 (pafi)</p>

The microstructure and consequently the mechanical properties of titanium alloys are highly dependent on the temperature history endured by the material. The manufacturing process of metal deposition induces repetitive cooling and heating in the material determining a specific microstructure. The presented study is devoted to developing and implementing a microstructure model for Ti-6Al-4V intended to be coupled to a thermo- mechanical model of the metal deposition process. Microstructural analysis of the metal deposited samples was first performed to understand the formed microstructure. A set of representative parameters for microstructure modelling were then selected as representative for the known impact of Ti-6Al-4V microstructure on mechanical properties. Evolution equations for these parameters were implemented for thermal finite element analysis of the process. Six representative state variables are modelled: the phase volume fraction of total alpha, beta, Widmanstätten alpha, grain boundary alpha, martensite alpha, and the alpha lath thickness. Heating, cooling and repeated re-heating involved in the process of metal deposition are taken into account in the model. The phase transformations were modelled based on a diffusionnal theory described by a Johnson-Mehl-Avrami formulation, as well as diffusionless transformations for the martensite alpha formation and the beta reformation during reheating. The Arrhenius equation is applied as a simplification to model temperature dependent alpha lath size calculation. Grain growth is not included in the present formulation, but would have to be added for capturing alpha lath coarsening during long term heat treatment. The temperature history during robotised tungsten inert gas deposition welding is simulated together with the microstructure. The implementation of the model handles well the complex cyclic thermal loading from the metal deposition process. A particular banded structure observed in the metal deposited microstructure is partially explained using the proposed microstructure model. It is concluded that although qualitatively interesting results have been achieved, further calibration testing over a wider range of temperature histories must be performed to improve the transformation kinetic parameters for reliable quantitative predictions of the microstructure. / <p>Godkänd; 2008; 20081128 (ysko)</p>

The simulation of hot extrusion processes is a difficult and challenging problem in process modeling. This is due to very large deformations, high strain rates and large temperature changes during the process. Computer models that with sufficient accuracy can describe the material behavior during extrusion can be very useful in process and product development. Today, the process development in industrial extrusion is to a great extent based on trial and error and often involves full size experiments. Numerical simulations can most likely replace many of these experiments, which are often both expensive and time consuming. The motivation for this research project is a request for accurate finite element models that can be used in process design and development of stainless steel tube extrusion. The models will be used to investigate the effect of different process parameters on the quality of the extruded tube. In the work presented in this thesis, thermo-mechanically coupled simulations of glass-lubricated tube extrusion were performed. Extrusion models in two and three dimensions were developed. Only extrusion problems with radial symmetry were considered. Simulations were carried out using the commercial code MSC.Marc, which is a Lagrangian finite element code. Frequent remeshing was therefore needed during the analyses. The models were validated by comparing predicted values of extrusion force and exit surface temperature with measurements from an industrial extrusion press. The two- dimensional model was shown to provide good and fast solutions to extrusion problems with radial symmetry. A two-dimensional model is sufficient for many applications and this model is planned to be used for solving process problems further on. For the three-dimensional model it was concluded that a very fine mesh would be needed to successfully predict the extrusion force using four-node tetrahedrons. This would result in unacceptably long computational times. The future work will be aiming at improving the three- dimensional model in order obtain accurate results within a reasonable time. To obtain reliable simulation results a good constitutive model is crucial. This work has focused on the use of physically based material models, which are based on the underlying physical processes that cause the deformation. It is expected that these models can be extrapolated to a wider range of strains, strain rates and temperatures than more commonly used empirical models, provided that the correct physical processes are described by the model and that no new phenomena occurs. Physically based models are of special interest for steel extrusion simulations since the process is carried out at higher strain rates than what are normally used in mechanical laboratory tests. A dislocation density-based material model for the AISI type 316L stainless steel was used in the finite element simulations included in this thesis. The material model was calibrated by data from compression tests performed at different temperatures and strain rates. / <p>Godkänd; 2006; 20070109 (haneit)</p>

How do we perceive the influence of the hand on the material in the things that surround us in our everyday life? This is a reflective thesis that addresses questions about the relations between human and machine and discusses our approach to the traces of the human hand and thought in the products we create and use. In this thesis, I try out a method which main purpose is to clarifiy which parts of the craft I think are most interesting, depending on how you choose to approach it. I have taken the role of the effective carpenter and the improvising carpenter. Based on these two roles I have built 4 stools. In my choices as the effective and the improvising carpenter, I have tried to visualize my own attitudes, values and approaches to my craft. The result of my survey has shown that there are interesting parts in both ways that I want to work with. Hopefully this thesis can serve to broaden and discuss the view of craftsmanship today.

The MAX phases constitute a group of ternary ceramics which has received intense attention over the last decade due to their unique combination of properties. The Ti3SiC2 is the most well studied MAX phase to date and it has turned out to be a promising candidate for high temperature applications. It is oxidation resistant, refractory and not susceptible to thermal shock, while at the same time it can be machined with conventional tools which is of great technological importance. Most attempts to synthesize bulk Ti3SiC2 have involved pure titanium in the starting powder mixtures, but Ti powder is oxidising and requires an inert atmosphere throughout the synthesis process which makes the procedures unsuitable for large scale production. The aim of the first part of this study was to delineate the influence of sintering time and temperature on the formation of Ti3SiC2 from a starting powder which does not contain pure titanium. Titanium silicon carbide MAX phase was synthesised from ball milled TiC/Si powders, sintered under vacuum for different times and temperatures. After heat treatment the samples were evaluated using scanning electron microscopy (SEM) and x-ray diffraction (XRD). This study showed that TiC was always present in the final products whereas TiSi2 was an intermediate phase to the Ti3SiC2 formation. The highest amount of Ti3SiC2 was achieved for short holding times of 2-4 hours, at high temperatures, 1350-1400¢ªC. More elevated temperatures or extended times resulted in silicon loss and decomposition of Ti3SiC2. In the second part of this study the sintering reactions and the mechanisms of formation of Ti3SiC2 were investigated by x-ray diffractometry, thermodilatometry, thermogravimetry, differential scanning calorimetry and mass spectrometry. TiC/Si powders of the different ratios; 3:2 and 3:2.2, were heated to different temperatures under flowing argon gas in a dilatometer and examined by XRD. The TiC/Si powder samples of the ratio 3:2 were further investigated by the other thermal analysis methods. The results confirmed the presence of the intermediate phase TiSi2. From 1500¢ªC silicon evaporation and MAX phase decomposition were observed, and the results show that the MAX phase formation may be concurrent with the melting of silicon. TiC was always present in the final products, either as a reactant or as a decomposition product. The extra silicon of the 3:2.2 TiC/Si powder significantly increased the Ti3SiC2 conversion and no intermediate phases were observed for this powder mixture. The Si of these samples did not melt or evaporate, and only minor decomposition was observed even at 1700¢ªC. These results indicate that the silicon content of the initial powder mixture is decisive to the reaction mechanisms of the sintering process. / <p>Godkänd; 2007; 20070523 (ysko)</p>

With an increasing demand for fossil-free energy the development of efficient solar cells made from sustainable and abundant materials is needed. A promising group of new absorber materials are the chalcogenide materials, including the chalcostibnite compounds copper antimony selenide, CuSbSe2. The few studies that have been carried out on this material show promising properties with an absorption coefficient higher than 7 x 104 cm-1 in the visible region and a band gap around 1.5-1.1 eV, which theoretically can be tuned by creating an alloy with the more studied and higher band gap material CuSbS2. This project has focused on creating CuSbSe2 using closed space vapor transport (CSVT) depositions. Three different approaches have been used; deposition of antimony selenide, Sb2Se3, on pre-sputtered copper films, deposition of antimony and selenium in two steps on pre-sputtered copper films and deposition of selenium on pre-sputtered stacked films of copper and antimony. The films were analyzed using optical imaging, SEM, EDS, XRD, and UV-Vis spectroscopy. It was found that the Cu-Sb-Se system is complicated, containing numerous phases with low crystallographic symmetry compared with chalcopyrite materials. The sublimation data found in the literature for Sb2Se3 is not applicable for the pressures used in this project. Created samples did not contain enough antimony and further studies on Sb2Se3 are needed if CuSbSe2 is to be created in the CSVT system using Sb2Se3 as source. In the three different experimental procedures used in the project, the phases CuSbSe2, Cu3SbSe3, Cu3SbSe4, Sb2Se3 and an unknown phase were observed in the samples. The composition of the unknown phase could not be identified but its XRD pattern has been revealed. The window in ratio of Cu:Sb for creating CuSbSe2 seems to be very narrow and needs to be close to 1:1. If so the phase can be formed by annealing samples consisting of  Cu3SbSe4 or Sb2Se3. A more refined approach where the deposition and reaction with selenium can be better controlled thus needs to be developed in order to form films with single phase CuSbSe2.

In classical description, the mechanical state of a material point depends on the variables defined at this point solely. It can integrate and catch some aspects of the material’s microstructure by conventional homogenization method. The application of the conventional continuum assumption results in a simplified description of the system which makes the large scale simulation of the material more efficient but at the expense of a loss of information at small length scales. Localization is a phenomena where a large degree of deformation occurs in highly concentrated regions. The conventional continuum theory with strain softening can not give the convergent solution as the size of the localization zone is completely determined by the mesh discretization. The multiresolution continuum theory (MRCT) is a higher order continuum theory where additional kinematic variables supplementing the conventional macroscopic displacement field are added to account for deformations at several distinct length scales. The direct inclusion of the length scale parameters in the material’s constitutive equations remedies the convergence problem. In crystalline materials the initiation of plastic flow and subsequent permanent plastic deformation is attributed to the presence and movement of dislocations and also the interactions between the dislocation themselves and different kinds of obstacles, inclusions, second phase particles and grain boundaries etc. Some of these defects can alsolead to damage initiation in the materials. For example, the stresses developed at the dislocation pile-ups contribute to the initiation of the microvoids and microcracks. A dislocation density based damage model has been developed and combined with a physically based flow stress model. They are calibrated and validated for 316L stainless steel at different temperatures and strain rates. These models have been implemented into the macroscopic material description of the MRCT element. / <p>Godkänd; 2016; 20160215 (haoqin); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Hao Qin Ämne: Materialmekanik/Material Mechanics Avhandling: Multiresolution Continuum Theory and Dislocation Density Based Constitutive Relations Opponent: Professor emeritus Kenneth Runesson, Avd för material- och beräkningsmekanik, Institutionen för tillämpad mekanik, Chalmers tekniska högskola, Göteborg. Ordförande: Professor Lars-Erik Lindgren, Avd för material- och solidmekanik, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå. Tid: Måndag 25 april, 2016 kl 09.30 Plats: E246, Luleå tekniska universitet</p>

Ductile fracture presents challenges with respect to material modelling andnumerical simulations of localization. The strain and damage localization maybe unwanted as it indicates a failure in the process or, as in the case ofmachining and cutting, a wanted phenomenon to be controlled. The latterrequires a higher accuracy regarding the modelling of the underlying coupledplastic and fracturing/damage behaviour of the material, metal in the currentcontext as well as the stability and robustness of the simulation procedure.This aim of this work is to develop, evaluate and implement formulations thatcan efficiently and reliably handle localization problems in machiningsimulations. The focus is on non-local models. The non-local models extendthe standard continuum mechanics theory by using non-local continuumtheory in order to achieve mesh independent results when simulating fractureor shear localization.The non-local damage model is implemented and various formulations areevaluated in a Matlab™ based finite element code. The chosen algorithm wasthen implemented in commercial software. The implementations remedy themesh sensitivity problem and gives convergent solution for metal cuttingsimulations with reasonable cost. The length scale associated with the nonlocalmodels are in the current context considered as a numericalregularization parameter. The model has been applied in machiningsimulations and compared with measurements from industry.Keywords: Finite element simulation; Non-local damage; Plasticity; Machining / Godkänd; 2016; 20160222 (oluabi); Nedanstående person kommer att disputera för avläggande av teknologie doktorsexamen. Namn: Olufunminiyi Abiri Ämne: Materialmekanik/Material Mechanics Avhandling: Non-Local Models in Manufacturing Simulations Opponent: Professor Miguel Vaz, Dept Mechanical Engineering, State University of Santa Catarina, Joinville, Brazil. Ordförande: Professor Lars-Erik Lindgren, Avd för material- och solidmekanik, Institutionen för teknikvetenskap och matematik, Luleå tekniska universitet, Luleå. Tid: Fredag 22 april, 2016 kl 09.30 Plats: E231, Luleå tekniska universitet

This work has concerned the preparation and properties of all-oxide composites. The most common examples of such materials are composites of oxide particles in an oxide matrix, continuous oxide fibres in an oxide matrix and layered composites consisting of alternate layers of different oxides. In the case of continuous fibre composites, the matrix and fibres can be of the same oxide since the mechanical properties of the composite are to a large extent influenced by the interface between the two. All-oxide composites are of interest as possible high temperature materials since they are inherently oxidation resistant. The emphasis of the thesis is on continuous fibre composites. The thesis, consisting of an extensive introductory review and six appended papers (listed in appendix 2), covers a number of aspects of these composites including the properties of candidate oxide constituents, methods of composite preparation, microstructure and mechanical properties. The first paper describes attempts made to prepare alumina composites reinforced with monocrystalline (sapphire) fibres using hot isostatic pressing. The second paper reports on the thermal expansion behaviour of candidate oxides and the consequences of differences in thermal expansion of composite constituents with respect to residual thermal stresses in the composite. Paper VI reports measurements made of the stress-strain and fracture behaviour of experimental sapphire fibre/alumina matrix composites. The materials studied included both unidirectional and 0/90° cross-ply composites, all with a thin layer of zirconia at the fibre/matrix interface designed to adjust the interfacial properties to provide optimum composite stress-strain behaviour. The results could be linked to measurements made of interfacial properties. Papers III, IV and V concern the stress strain behaviour of a commercial all-oxide composite consisting of fine-diameter, polycrystalline oxide fibres in a porous, aluminosilicate matrix. In these composites the fibres were woven in a 0/90° geometry and tested in both the 0/90° and ±45° orientation. The emphasis of the study was on the notch-sensitivity of test specimens containing a central circular hole. Aspects studied included failure mechanisms, the effects of notch size and the effects of high temperature thermal exposure on microstructure and strength degradation. The observed behaviour could be described successfully in terms of a simple model based on fracture mechanics. / Godkänd; 2001; 20060917 (cira)

This doctoral thesis covers investigation of the surface phenomena of Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo alloys related with oxidation at elevated temperature and corrosion duringchemical treatment in hydrofluoric-nitric acid (HF/HNO3) solutions. The explored phenomenaare related to manufacturing and service conditions of aero-engine components. Duringmanufacturing and operation, the alloys are running at elevated temperatures in oxygencontaining environment. Under these conditions there are formations of an oxide on the surfaceand an oxygen enriched layer below the oxide, commonly referred as alpha-case. The alpha-caseis a hard and brittle layer that is detrimental to the mechanical properties and must therefore beminimized or completely eliminated. A conventional method for elimination of alpha-case ischemical processing in HF/HNO3 solutions, known as chemical milling.Isothermal oxidation treatments in air at 500, 593 and 700 ºC for up to 500 hours were carriedout in this study. Both alloys developed rutile type of oxide structure and Ti-6Al-2Sn-4Zr-2Moexhibited stronger oxidation resistance than Ti-6Al-4V. Transition from parabolic to linearoxidation rate was observed at 700 ºC and ≥ 200 hours for both alloys. The difference in theoxidation kinetics of the two alloys is suggested to be related with the chemical composition ofthe alloys. The oxygen enriched layer, i.e. alpha-case layer, was characterised and its thicknesswas measured using conventional metallographic and microscopic techniques. Parabolicrelationship of the alpha-case layer growth rate with time was observed for both alloys. Theoxygen diffusion parameters and activation energies were estimated in the temperature range of500-700 ºC. Additionally, the oxidation at 700 ºC for 500 hours resulted in microstructuralchanges and element re-distribution. The bulk and alpha-case layer hardness at micro- and nanoscalewere measured using microhardness and nanoindentation techniques. The alpha-case layerhad higher hardness due to the solid solution strengthening effect of the diffused oxygen.The effect of chemical milling in 1:11 HF/HNO3 solution on the surface integrity, and theinfluence on low cycle fatigue (LCF) strength of cast Ti-6Al-2Sn-4Zr-2Mo alloy wasinvestigated. Short and long chemical processing times (5 and 60 minutes) and three imposedtotal strain ranges in fatigue tests were evaluated. Significant drop in fatigue life was observedfor the samples etched before LCF testing, as compared to the non-etched samples. The influencefrom etching was found to be most detrimental for fatigue samples tested at the lowest strainranges. The fatigue life reduction was correlated with the number of crack initiation sites.Multiple crack initiation sites were observed for the etched samples, whereas only one crackinitiation site was discerned in the non-etched samples. Inspection of the surface of the etchedsamples revealed selective and severely etched prior β grain boundaries and pit formation at thetriple joints of the prior β grain boundaries. These surface defects were considered as stressraisers promoting an earlier fatigue crack initiation.The influence of two different molar concentration ratios (1:3 and 1:11) of HF and HNO3acids on the corrosion behaviour of cast Ti-6Al-4V and Ti-6Al-2Sn-4Zr-2Mo were investigatedusing electrochemical and atomic force microscopy (AFM) techniques. The corrosion of the twoalloys was a function of the HF/HNO3 concentration ratio and also of the alloys’ chemicalcompositions. The AFM measurements revealed selective and faster dissolution rate of the α-phase than the β-phase in the Widmanstätten microstructure. It was considered that the reason forselective dissolution was the formation of local micro-galvanic cells between the α-phase and theβ-phase. Moreover, the Volta-potential was measured using scanning Kelvin probe forcemicroscopy (SKPFM) and the obtained maps revealed difference in the Volta-potential betweenvithe α-laths and the β-laths in both alloys. This observation strengthened the likelihood forformation and operation of micro-galvanic cells between the α-phase and the β-phase when thealloys were in contact with HF/HNO3 solution.Keywords: Titanium alloys, oxidation, oxide, alpha-case, chemical milling, corrosion.